An internal combustion engine refers to an engine in which combustion gas generated by the combustion of fuel directly acts on a piston or a turbine blade and the like to convert thermal energy of the fuel into mechanical work. Although it commonly refers to a reciprocating type engine that ignites a gas mixture of fuel and air and explodes it in a cylinder to move a piston, a gas turbine, a jet engine, rocket and the like also fall within an internal combustion engine.
According to the type of fuels, the internal combustion engine may be classified into a gas engine, a gasoline engine, a petroleum engine, a diesel engine, and the like. For instance, the petroleum⋅gas⋅gasoline engines ignite into electric spark by a spark plug, and the diesel engine sprays fuel into high temperature and high pressure air to spontaneously ignite. The internal combustion engine may also be classified into 4-stroke and 2-stroke cycle types according to the stroke⋅movement of a piston.
Commonly, the internal combustion engine of a vehicle has been known to have thermal efficiency of about 15% to 35%, and even at the maximum efficiency of the internal combustion engine, due to thermal energy and exhaust gas discharged outside through the wall of the internal combustion engine, about 60% or greater of the total thermal energy may be wasted.
As such, if the amount of thermal energy discharged outside through the wall of an internal combustion engine is reduced, the efficiency of an internal combustion engine may increase, and thus, methods of installing thermal insulation material outside of the internal combustion engine, modifying a part of the material or structure of the internal combustion engine, or developing a cooling system of the internal combustion engine have been used.
Particularly, when discharge of heat that is generated inside the internal combustion engine outside through the wall of the internal combustion engine is minimized, the efficiency of the internal combustion engine and the fuel efficiency of an automobile may be improved. However, there have been insufficient studies on thermal insulation material or thermal insulation structure that can be maintained for a long time inside the internal combustion engine to which high temperature and high pressure conditions are repeatedly applied.
Accordingly, there is a demand for the development of novel thermal insulation material that has low thermal conductivity and excellent heat resistance, and when applied for an internal combustion engine, can be maintained for a long time.